48x18 vs 48x19

46:18 = 63.6GI
48:18 = 66.4GI

You wouldn't really notice the difference. Both above would be a lot spinnier to what you're currently riding. You're better off changing the cog.

48:17 = 70.3GI
48:16 = 74.6GI
48:15 = 79.6GI

Nice one cheers!

I think I may just get a 17T and an 18T and try both out to see which will suit me best